Sure. I'll take all constructive information. But what don't you like about the cover? I asked a lot of people for feedback on it before it went up, and the response was all positive.

Yeah, I don't much care for the cover either. Take the rest with a grain of salt, as it's all just my unfiltered opinion:

The red and blue on black isn't pleasing.
The font is... odd. It looks unprofessional, but I don't know why. (I'm not in graphic design, nor do I know my typefaces.)
The black/blue skewed square gives it a diamond-patterning effect, which I just don't like. If the black didn't extend all the way to the edges I think it would look ok.
The wacky psychedelic graphic makes the cover look dated to me. And it reminds me of the unpleasant screen saver from Windows 3.11.

EDIT to add:
The cover also doesn't tell me anything about your book. "Neptune" implies some sort of water or space-related theme, but the cover doesn't give me any feel for the content of the book.